Compressor



Aug. 20, 1957 K. A. DARROW COMPRESSOR 2 Sheets-Sheet 1 Filed Sept. 29,1954' Fig.2.

inventor.- .Kenneh A parrow, by 4 United States Fatent @rfrce massesPatented Aug. 20, 1957 CGMPRESSOR Kenneth A. Darrow, Sprakers, N. Y.,assignor to General Electric Company, a corporation of New YorkApplication September 29, 1954, Seriai No. 459,042

4 Claims. (Cl. 236-114) This invention relates to compressors and moreparticularly to a method and apparatus for eliminating pulsation in suchcompressors.

Pulsation is an unstable, intermittent flow condition in which there isa cyclic reversal of flow caused by excess flow-throttling. Thiscondition is a serious limitation in the operating range of acentrifugal or axial flow compressor because it greatly reducescompressor performance at low rates and limits the minimum flow ratepossible. Such pulsation occurs when the flow rate in the compressor hasbeen reduced to some value below the designed operating point of themachine either by throttling the inlet or outlet thereof. Flow in boththe impeller and diffuser of the compressor becomes completely separatedalong the full length of the flow passages to produce pulsation. Inlarge compressors, the efiect may become so violent that the machineisdestroyed thereby.

Accordingly, it is an object of my invention to provide anovel apparatusto eliminate compressor pulsation.

It is another object of the invention to provide an improved difluserstructure which will eliminate vpulstlf On in the compressor.

It is another object of the invention to provide animproved compressorwith a stable non-pulsating flow from normal flow to zero flowconditions.

It is another object of the invention to provide an improved compressorin which higher efficiencies are maintained at the low flow range nearor below the normal pulsation point.

It is a further object of the invention to provide a novel method ofeliminating pulsation in a compressor.

In carrying out my invention in one form a flexible diffuser wall isprovided in the compressor to give a correct variable area ratio for allcompressor flows.

These and various other objects, features and advantages of theinvention will be better understood from the following description takenin connection with the accom panying drawing in which:

Fig. 1 is a sectional view of a centrifugal compressor which embodies myinvention;

Fig. 2 is a sectional view similar to Fig. l with the flexible wall in aclosed position;

Fig. 3 is a sectional view of a centrifugal compressor in which thefluid has partially separated from the walls;

Fig. 4 is a sectional view similar to Fig. 3 in which the fluid hascompletely separated from the walls;

Fig. 5 is a sectional view similar to Fig. 4 in which a flexible memberis provided to produce the correct difiuser area ratio;

Fig. 6 is a graph of compressor pressure rise plotted against fluid flowat variable speed; and

Fig. 7 is a graph of compressor pressure rise plotted against fluid flowat constant speed.

In Fig. 1 of the drawing, a centrifugal compressor is shown generally at10 which comprises a casing 11 to define a chamber 12 therein. Casing 11is provided with an upper wall 13 in which an air inlet or aperture 14is centrally disposed. An electric motor 15 is secured at the marginaledge of opening 14 and vertically spaced there from by means of suitablespacing elements 16 and bolts 17. Motor 15 has a shaft 18 to projectdownwardly into chamber 12. A centrifugal blower impeller 19 with aplurality of curved blades 20 is mounted on shaft 18 to drive air frominlet 14 downwardly and outwardly toward the inner wall of casing 11.

A vaneless diffuser 21 surrounds impeller 19 to provide a back wall 22and a forward wall 23. A flexible wall 24 is positioned on the innersurface of back wall 22 and secured thereto adjacent the difluser inletby any suitable means, such as, for example, by screws 25. If it isdesired, either wall 22 or 23 could be composed of flexible material toeliminate wall 24. The periphery of flexible wall 24 is provided with aplurality of spaced apertures for purposes to be explained hereinbelow.

An aperture 26 is provided in wall 13 in axial alignment with each ofthe apertures in flexible wall 24. A casing 27 is fitted over eachaperture 26 and secured to wall 13 by means of screws 28. A vent 29 islocated in casing 27 to communicate with the atmosphere. A flexiblemember 39 is positioned across aperture 26 to provide a diaphragm towhich a rod 31 is secured by a nut 32. The opposite end of rod 31 isretained in the aperture in wall 24 by a pair of nuts 33. An adjustablescrew 34 extends through casing 27 to provide a support for a spring 35which is connected to the opposite side of diaphragm 30.

In Fig. 2 of the drawing, flexible member 24 is shown in contact withwall 23 to provide a closure for the outlet of diffuser 21. Such aclosure is produced by an increase in pressure in chamber 12 which isexerted against diaphragm 30 to force spring 35 outwardly. A partial closure is attained when compressor 10 approaches the zero flow conditionto provide only a small exit area which maintains the high velocity flowfrom the difluser outlet.

In Fig. 3, fluid, which is designated by arrows 40, is forced from theair inlet through impeller 19 and diffuser 21 toward the inner wall ofthe compressor casing. Initial separation of the fluid from the walls ofthe impeller and diffuser is shown by areas 41 and 42. Arrow 43designates the fluid which has separated from the impeller wall andreversed its direction of flow.

In Fig. 4, pulsation conditions are shown in compressor 10 which is notprovided with a flexible member 24 to break a continuous low kineticpath 44. Path 44 is produced by complete separation of fluid along thefull length of the flow passage. Pulsation is caused by a feedbackthrough path 44 of air which is designated by arrows 45.

In Fig. 5, flexible member 24 is positioned adjacent wall 23 of diffuser21 to produce the correct diffuser area ratio for this flow condition.Such closure prevents separation and pulsation which would occurotherwise.

In the operation of compressor 11 in Figs. 1 and 2, centrifugal actionof impeller blades 20 drives air which comes in inlet 14 downwardly andoutwardly toward the inner wall of casing 11. While a constant flow rateis provided in compressor 10, flexible member 24 remains injuxtaposition with diffuser wall 22 to allow fluid flow to proceedthrough the outlet of diffuser 21. When flow is reduced, motor 15 isunloaded to increase the speed and pressure. Difierential pressurebetween chamber 12 and the atmosphere moves diaphragm 30 to operateflexible member 24 which provides the correct difl'fuser area ratio forany particular flow. The position of member 24 allows full flow throughthe diffuser outlet to prevent separation. When fluid flow returns toits normal Value, a decrease in pressure in chamber 12 allows diaphragm30 to return to its original position. Thus, rod 31 is pushed downwardlyby spring 35 to move flexible member 24 adjacent wall 22. The diffuseroutlet remains open until a subsequent decrease of fluid flow occurs.

is reduced in a conventional compressor below the design point,separation begins at areas 41 and 42. In Fig. 4, complete separation hasresulted in pulsation which is caused by feedback through the lowkinetic energy path 44 of air which is designated by arrows 45.

In Fig. 5, flexible member 24 prevents complete separation and pulsationin compressor because a correct diffuser area ratio is maintained forany particular flow. Thus, there is no low kinetic energy path throughwhich an air feedback occurs. If compressor 10 operates at a constandspeed, a Pitot tube could be used to measure the change in velocity headwith the change of fluid flow to operate diaphragm 30.

In Fig. 6, a graph of compressor pressure rise in head inches of Water(H2O) is plotted against fluid flow in cubic feet per minute at variablespeed. The speed of the impeller increased as the loadrwas decreasedwith decreasing flow. .As the normal pulsation point was approached,difiuser area ratio was decreased enough to give the correct area ratioto prevent separation. This. area ratio was progressively decreased withdecreasingfiow to the zero flow point. The primary reason that pressureincreased with decreasing flow is the increased speed of the impeller. 1

In Fig. 7, a graph of compressor pressure rise in head inches of water(H2O) is plotted against fluid flow in cubic feet per'minute at aconstant impeller speed of 15,000 revolutions per minute. This graphdiscloses the increase in, operating range below the normal pulsationpoint which results from the use of flexible member 24.

As will be apparent to those skilled in the art, the objects ofmy-invention are attained by the use of a flexible diffuser wall whichprovides a correct variable area ratio for all compressor flows.

While other modifications of this invention and variations of apparatuswhich may be employed within the scope of the invention have not beendescribed, the invention is intended to include all such as may beembraced within the following claims.

What I claim as new and desire to secure by Letters tioned in saidcasing wall and connected to said rod, and biasing means to return saidannular member to its unflexed position.

2. Pulsation control means for centrifugal compressors and the likecomprising in combination, an annular diffuser surrounding and arrangedto receive fluid from an impeller, said ditfuser having a spaced apartback and forward wall, an annular casing encircling said difiuser, anannular flexible member positioned adjacent one of said walls withinsaid diflt'user, the inner circumference of said annular member beingaflixed to its associated wall and the outer circumference being freefor movement, and a pulsation sensitive device in said casing andattached to the free circumference of said annular member, whereby upona pulse pressure rise in said casing, said pulsation sensitive deviceacts upon said annular memher to reduce the cross-sectional area betweensaid diffuser walls to prevent the formation of pulsation conditions.

3. The invention as claimed in claim 2 wherein said pulsation sensitivedevice includes a diaphragm positioned in the wall of and sensitive topressure variations within said casing, a rod connecting said diaphragmand the free end of said annular member, and spring means for biasingsaid rod to maintain said annular member in an unflexed condition.

4. The invention as claimed in claim 3 wherein said pressure sensitivedevice includes adjusting means for varying the force applied by saidbiasing means, and means associated with said rod and the free end ofsaid annular member for adjustably positioning the annular member insaid difiuser.

References Cited in the file of this patent UNITED STATES PATENTS1,095,767 Adams May 5, 1914 1,188,995 Rice June 27, 1916 1,401,668 Brownet a1 Dec. 27, 1921 1,620,111 Lewis Mar. 8, 1927 2,285,976 Huitson June9, 1942 2,648,195 Wilde'et al Aug. 11,1953 2,684,634 Schneider July 27,1954 FOREIGN PATENTS 50,411 France Mar. 12, 1940 (Addition to 829,826)

285,815 Great Britain May 17, 1928 305,214 Great Britain Jan. 29, 1949611,726 Great Britain Nov. 3, 1948 875,086 France June 8, 1942

